The present invention relates to a method for continuous casting of a metal as well as an apparatus therefor. More particularly, the invention relates to an improved method and apparatus for continuous casting of a metal capable of giving a continuouslength bar ingot of the metal having a unidirectionally solidified metallographic structure free from defects and segregation of impurities as well as smooth surface.
Along with the rapid progress of high technologies in recent years, the demand for a further and further improved quality of metallic materials is also increasing year by year. Such a demand has no exception for a ontinous-length bar material of metal ingot prepared by a process of continuous casting. Notwithstanding the increasing demand for upgrading, the products prepared by a conventional process of continuous casting have several problems and defects unless or even when a special means is added to the apparatus for the continuous casting. For example, the solidification of the molten metal in the conventional process of continuous casting always starts at the inner wall surface of the tubular casting mold and the growth of the solidified crust proceeds toward the center axis so that the solidified body is composed of a large number of cubic crystals and the structure thereof can rarely be formed of single crystals. Moreover, the bar ingot sometimes contains a large number of blowholes or the surface of the bar ingot is sometimes roughened due to the friction between the moving bar ingot and the inner walls of the tubular casting mold.
An improved method and apparatus for continuous casting of a metal are disclosed in Japanese Patent Publication 55-46265. The improvement disclosed there may provide the most promising way among the many proposals and attempts hitherto made, all of which, however, could give no fundamental solution of the problems. In this method and the apparatus used therefor, the temperature of the inner surface of the tubular casting mold at the exit is kept higher than the solidification temperature of the melt of the metal under casting. This method, therefore, involves a danger of break-out and can be performed only under very troublesome control of various operating conditions since no solidified crust can be formed inside the casting mold and a solidified crust is first formed only at a certain height below the exit out of the casting mold.